D,L-2-amino-4-(hydroxymethylphosphinyl)-butanoic acid (abbreviated as DL-AMPB herein) is a well known compound having a herbicidal activity, and is used as an effective herbicide having a broad-spectrum (JP Patent Kokai JP-A-52-139727). However, it has been shown that the herbicidal activity of DL-AMPB is about one-half that of L-2-amino-4-(hydroxymethylphosphinyl)-butanoic acid (abbreviated as L-AMPB herein), and the essence of the activity is L-AMPB (JP Patent Kokai JP-A-55-000025, JP Patent Kokai JP-A-59-219297). Therefore, there is a strong desire to develop an efficient method for producing L-AMPB selectively.
Conventionally known methods for producing L-AMPB include (a) methods making use of microorganisms, enzymes, and (b) asymmetric synthesis methods. As the methods (a), there are disclosures such as a method for producing L-AMPB from 4-(hydroxymethylphosphinyl)-2-oxobutanoic acid with transaminase (JP Patent Kohyo JP-A-2003-528572) and a method for subjecting N-acetyl-DL-AMPB to enzymatic racemic resolution to produce L-AMPB (JP Patent Kohyo JP-A-2003-505031). However, in all of these methods, there are problems such that the reaction needs to be carried out at a low substrate concentration, complicated processes of aftertreatment and purification are required, and further an equimolar or more amount of expensive optically active amino acid(s) must be used in the transamination. There are disclosures, as the asymmetric synthesis methods (b), such as a method for alkylating (R)-3-isopropyl-2,5-dialkoxy-3,6-dihydropyrazine to synthesize L-AMPB (JP Patent Kokai JP-A-62-132891, and Tetrahedron Lett. 1255 (1987)) and a method for converting L-vinylglycine into L-AMPB stereospecifically (Tetrahedron Lett. 8263 (1992)). However, expensive optically active amino acids such as D-valine and L-vinylglycine need to be used for a starting material in these methods. Therefore, there are problems concerning inexpensive supply of raw material(s) in large quantities. Moreover, there are disclosed asymmetric synthesis methods such as a method for producing L-AMPB by subjecting 2-acetamide-4-(hydroxymethylphosphinyl)-butenoic acid to asymmetric hydrogenation reaction (JP Patent Kokai JP-A-62-226993, and J. Org. Chem. 56, 1783 (1991)). In this method, the asymmetric hydrogenation reaction is carried out using a rhodium catalyst comprising an optically active diphenylphosphine compound as a ligand. Therefore, it is thought that this method is efficient in terms of the use of chiral source in a catalytic amount. However, there is a problem such that optical yield is not high in this method.
On the other hand, asymmetric hydrogenation reaction to convert dehydroamino acid into amino acid using the rhodium catalyst in general is well known already (Chem. Rev., 103, 3029-3070 (2003)). However, most of the reactions are asymmetric reductions against dehydroamino acid having alkyl group and aryl group at side chain(s), and reactions using dehydroamino acid having highly polar substituent at side chain(s) are scarcely exemplified.
[Patent Publication 1] JP Patent Kokai JP-A-52-139727
[Patent Publication 2] JP Patent Kokai JP-A-55-000025
[Patent Publication 3] JP Patent Kokai JP-A-59-219297
[Patent Publication 4] JP Patent Kohyo JP-A-2003-505031
[Patent Publication 5] JP Patent Kokai JP-A-62-132891
[Patent Publication 6] JP Patent Kokai JP-A-62-226993
[Non-patent Document 1] Tetrahedron Lett. 1255 (1987)
[Non-patent Document 2] Tetrahedron 8263 (1992)
[Non-patent Document 3] J. Org. Chem. 56, 1783 (1991)
[Non-patent Document 4] Chem. Rev., 103, 3029-3070 (2003)